diff --git a/erpnext/education/doctype/course_enrollment/course_enrollment.py b/erpnext/education/doctype/course_enrollment/course_enrollment.py
index a70d40d..d521828 100644
--- a/erpnext/education/doctype/course_enrollment/course_enrollment.py
+++ b/erpnext/education/doctype/course_enrollment/course_enrollment.py
@@ -20,4 +20,13 @@
 		progress = []
 		for topic in topics:
 				progress.append(student.get_topic_progress(self.name, topic))
-		return reduce(lambda x,y: x+y, progress) # Flatten out the List
\ No newline at end of file
+		return reduce(lambda x,y: x+y, progress) # Flatten out the List
+
+	def validate_duplication(self):
+		enrollment = frappe.get_all("Course Enrollment", filters={
+			"student": self.student,
+			"course": self.course,
+			"program_enrollment": self.program_enrollment
+		})
+		if enrollment:
+			frappe.throw(_("Student is already enrolled."))
\ No newline at end of file